This invention relates to a simple but accurate remote speedometer-tachometer for measuring the speed of a craft and/or revolutions per minute of an engine mounted in said craft which produces a characteristic audible output pulse therefrom.
There are many types of speedometers and tachometers which physically attach to the engine in some manner to provide revolutions per minute (RPM) and speed indications. There are many applications, however, where direct physical attachment is either impossible or impractical, and these applications generally relate to those uses which require remote measurements. In order to make the remote measurements using very simple types of equipment, such systems are plagued with noise of various types, whether audible, inaudible, random or coherent, which prevent proper and accurate measurement. In light-operated tachometers, for example, stray light reflections and varying shadows, particularly, make low frequency measurements difficult. Microphone-operated tachometers, in which the output signal of the microphone used to monitor the exhaust of an engine or some other sound from the engine, are susceptible to interference from external sounds other than that of the engine being tested. In order to reduce such interference, the system for processing the signals generated by the tachometer would of necessity approach in sophistication that of a small computer to alleviate some of the interference problems. Remote speedometers usually involve radar or micorwave units which are expensive and do not measure rpm's.
Accordingly, it is an object of the present invention to provide a remote speedometer-tachometer which is simple, easy to operate, and provides a relatively accurate means for measuring the rpm's of an engine and/or the speed of the craft containing the engine.
Another object of this invention is to provide a new and novel remote speedometer-tachometer requiring no physical contact between the measuring instrument and the source being measured.
A further object of this invention is to provide a remote speedometer-tachometer in which the speed and/or RPM's can be measured from a single position with a small portable instrument.
Still a further object of this invention is to provide a remote speedometer-tachometer where the measurements can be made even in a field with high interference levels.